The present invention relates to a pressure-sensitive transfer recording medium, and more particularly, to a pressure-sensitive transfer recording medium adapted to overlapping strike printing such as over-strike or multi-strike printing on a low-noise impact type typewriter or printer.
For many years, office rooms have been places where business machines generating uncomfortable noises, such as typewriters or high-speed impact printers, are placed. When a number of such machines are placed together in one room, cumulative noises tend to do harm to the health or mental conditions of the workers serving in the room.
Under the circumstances, some attempts have been made to reduce such noises, including one wherein an impact printer is contained within a muffling covering and another wherein a low-noise printer is designed on the basis of non-impact printing techniques such as ink-jet printing and thermal transfer printing.
On the other hand, official standards on the maximum allowable noise level in offices have been provided.
Generally, an impact printer generates an average noise of 70 to 80 dB or more. The noise is of an impacting characteristic and generated mainly when a hammer is driven to impact against a pad of typefaces so that the pad is forced to be pressed against an ink ribbon superposed on a printing paper placed on a platen by a force sufficient to transfer the ink to the printing paper from the ink ribbon.
Recently, there have been put on the market new types of serial impact printers wherein noise generated due to impact during a printing operation is sharply reduced (refer to JP,A,62-7572, JP,A,62-7573, JP,A,62-7574, JP,A,62-9969 and JP,A,62-132649).
Ink ribbons usable in serial impact printers include a correctable ink ribbon and a multi-strike ink ribbon. In the case of the former, conventional ones gives images of a high quality but in the case of the latter, conventional ones are of no practical use.
Conventional multi-strike ink ribbons include one which has on a foundation a porous layer composed of porous particles and a resinous binder material for bonding the porous particles to each other, and containing a liquid ink paste which contains a mineral oil and an aliphatic amine salt as a wetting agent, each being incompatible with the resinous binder material, as the main components of the vehicle thereof, and has a viscosity of 4,000 to 10,000 cp at ordinary temperature, as shown in JP,A,58-29694. JP,A,63-309567 discloses the use as the above-mentioned liquid ink paste of one wherein the main component of the vehicle is a dimer acid and the viscosity of the paste is adjusted to a range of 5,000 to 25,000 cp at ordinary temperature. JP,A,61-24486 discloses to the use as the above-mentioned liquid ink paste of one wherein the main component of the vehicle is a liquid fatty acid and the viscosity of the paste is adjusted to a range of less than 4,000 cp at ordinary temperature.
However, such conventional multi-strike ink ribbons are of no practical use on the low-noise impact printer, because the optical density of images sharply decreases for repeated overlapping strikes. This tendency is remarkable with the ink ribbon disclosed in JP,A,61-24486 using an ink paste of a low viscosity and the ink ribbon cannot be used practically.
Recently there is a demand for a multi-strike ribbon which can be used satisfactorily under circumstances at low temperatures of not more than 10.degree. C.
It is an object of the present invention to provide a pressure-sensitive transfer recording medium which can give clear images for a multiplicity of overlapping strikes on a low-noise impact printer under low-temperature circumstances as well as under normal circumstances.